How to select currency and currency symbol?

Ecwid supports all the official currencies, which means you can set your products prices exactly in the currency you want to accept in your store. To do that please log in to your Ecwid control panel. Then go to the Settings → General → Regional Settings page. Find your currency in the Currency drop-down menu and set the necessary currency sign. If the selected currency has an official prefix, it will be added to Currency symbol prefix field automatically.

What is conversion rate field for? Why do I need to set conversion rate?

There is also a field used to convert order totals to dollars if payment gateway or shipping carrier accepts dollars only. For example if you use PayPal Standard and it doesn't accept payments in your currency, Ecwid will be able to convert the order total into dollars and send the request to PayPal.

So even if your use payment gateways that accept the currency you sell in, there is still the point with the shipping companies. If you sell your goods internationally, one day you may need the services of an shipping carrier, that does not accept your currency, but works with USD. In such a case you will need a conversion rate - due to it your customers will see the correct actual shipping rate in the currency of your shop and your shipping costs will coincide the shipping prices in your store.